Tyvek® proprietary nonwoven fabric is one and one-half times more effective at holding out the passage of particles greater than 0.5 µm than a calendered, high-density taffeta fabric, and three times as effective as a herringbone fabric. Results are based on industry standard testing conducted by an independent laboratory. Even with advances in reusable cleanroom fabric technology IsoClean® made with Tyvek® remains significantly better in blocking the passage of particles.

Introduction

Control of employee-generated particle contamination is an essential performance requirement of cleanroom garments. Three of the most common sources of employee generated contamination are skin flakes, street clothing and cosmetics. Passage of these particles through the cleanroom garment and onto the product being produced is a critical concern, especially in the manufacture of pharmaceuticals and other drugs. Understanding differences in fabric performance and implementing a garment system appropriate for the end use is a crucial step in overall contamination reduction. With advances in technology, new and improved reusable cleanroom garments are being introduced and promoted as providing a high level of barrier protection. This study was performed to compare the performance of Tyvek® 1422A to a typical herring bone weave, considered the "workhorse" in cleanroom fabrics, and to a high-density tafetta weave, calendered reusable fabric.

Experimental

Testing was performed at an independent facility with expertise in testing and analysis for the cleanroom industry. The particle penetration test was performed in accordance with IES-RP-CC003.2 "Garment Considerations for Cleanroom and Other Controlled Environments," Section 7.3.1. The tests are performed in a non cleanroom environment using the ambient aerosol (room air) as the challenge. The test fabric is mounted in a filter holder having a 25 cm diameter active filtration region. A vacuum pump is used to establish flow through the fabric at a rate that yields a pressure drop of 1 cm H20. An aerosol particle counter is used to sequentially obtain ten l-minute upstream and ten l-minute downstream samples. From the particle counter, the filtration efficiency of the fabric is computed for particles >0.5 µm. The test is repeated and a second set of filtration efficiency values are computed. If the efficiency values are not within 15%, the test is repeated until the values are within 15% and the average of the two values is computed and reported.

The particle counts were obtained with a Climet Instruments Model 226/8040 aerosol analyzer. The sampling rate was 0.25 cfm (7.1 L/min.). The counter samples particles from 0.3-10 µm in 16 sizing channels. The counter was calibrated by sampling monodisperse aerosol particles of known size. The pressure drop across the fabric was measured with Dwyer Instruments Inc. Series 2000 Magnehelic Differential Pressure Gauge (0-10 H20). Calibration was verified by comparison to an inclined manometer. Flow rate through the test fabric was measured with Dwyer Instruments Inc. Model RMA-8 for 10-100 scfh (5-50 L/min.) and Model RMC-105 for 60-600 scfm (30-300 L/min.).

Three garment types were tested: two wovens and one nonwoven. Five samples were taken from each material type. A total of 15 samples was tested. All garments were cleaned and sterilized prior to testing. In addition to the 15 sample runs, control tests were run with HEPA media to ensure ability to measure a 100% efficient media, and "no filter" tests were run to ensure ability to measure 0% efficiency.

Results

As stated in the IES test procedure, all tests were performed at a constant pressure drop of 1.0 cm H20. From the flow rate and ten upstream and ten downstream aerosol concentration measurements, the following values were computed:

               Average Downstream Particle Count
Penetration = ——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;
                Average Upstream Particle Count

                  Volumetric Flow Rate @ 1cm H20
Face Velocity = ——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;——mdash;
                   Active Filtration Area

Since the permeability of the fabrics varied, a penetration velocity was also calculated:

* Numbers in parentheses represent standard deviation.

Conclusions